Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $97.27   8.807%   $105.8366   $105.84   $105.85   $105.80  
  Purchase #2 $96.53   10.475%   $106.6415   $106.64   $106.65   $106.60  
  Purchase #3 $247.58   6.510%   $263.6975   $263.70   $263.70   $263.70  
  Purchase #4 $204.91   5.544%   $216.2702   $216.27   $216.25   $216.30  
  Purchase #5 $122.46   9.426%   $134.0031   $134.00   $134.00   $134.00  
  Purchase #6 $99.46   8.409%   $107.8236   $107.82   $107.80   $107.80  
  Purchase #7 $76.54   5.127%   $80.4642   $80.46   $80.45   $80.50  
  7 purchase totals = $944.75       $1,014.7367   $1,014.73   $1,014.70   $1,014.70